Field of the Invention
This invention relates to implantable biomedical interfaces for the peripheral nervous system, and more particularly to a cuff for biologic soft tissue that can be used to optically stimulate axons in a single fascicle without damaging the nerves.
Description of the Related Art
The peripheral nervous system (PNS) consists of the nerves outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system (CNS) to the limbs and organs, serving as a communication relay between the brain and the extremities. The PNS includes motor nerves for motor control, sensor nerves for sensory functions such as touch, temperature, pressure, vibration and shear and autonomic nerves for such functions as controlling heart rate, digestion, immune system, flight or fight, etc. A peripheral nerve bundle for a particular function (sensory, motor, autonomic) includes multiple fascicles for different regions of the body with each fascicle including multiple axons (e.g. 10,000 to 100,000) for different functional sub-modalities (e.g. touch, temperature, pressure, etc.). The peripheral nerve bundle will branch out as it extends to the extremities, possibly to a single fascicle.
Biomedical devices and therapies are evolving that target the precise application of stimuli to specific nerve modalities and sub-modalities and recording of the effects of their stimulation. Such devices and therapies may be used as an interface for prosthetic devices to restore lost sensory or motor function, to augment human sensory or motor performance or to modulate autonomic functions.
Cuff electrodes have been used to provide a neural interface for direct electrical stimulation of peripheral nerves. One type of cuff is a soft tissue cuff that is placed around the peripheral nerve bundle and is non-invasive to the soft tissue.
U.S. Pat. No. 6,456,866 entitled “Flat Interface nerve electrode and a method for use” and referred to as FINE discloses a plurality of conductive elements embedded in a non-conductive cuff structure, which acts to gently redefine the geometry of a nerve through the application of a force so as to apply pressure to a nerve. The cuff has an opening, which is elongated relative to the diameter of the nerve to which it is applied. Preferably, the cuff is constructed from an elastic biocompatible material having top and bottom beam members configured to define a nerve opening. The cuff is open at one side and has a connection at the other side, which results in a spring force being applied through the surfaces of the nerve opening to the subject nerve. During implantation the open sides of the cuff are closed so as to capture the nerve in the cuff. As the nerve is reshaped, specific nerve axons become more easily addressed through the epineurium by the embedded conductive elements. Flattening the nerve provides selectivity, i.e. the ability to activate and record a specific population or subset of axons within a nerve.
Anthony V. Caparso et. al. developed a variant on the FINE know as the Slowly Closing—FINE or SC-FINE as described in “A nerve cuff electrode for controlled reshaping of nerve geometry” Journal Of Biomaterials Applications Volume 24—September 2009 pp. 247-273. The SC-FINE provides more precise control over the rate of closure and the gradual reshaping of the peripheral nerve bundle. The SC-FINE combines the reshaping properties of the FINE and the controllable degradation of poly DL lactic-co-glycolic acid (PLGA). A PLGA film is bonded to a stretched FINE. As the film degrades in-situ, the FINE returns to its original geometry and gradually reshapes the peripheral nerve bundle.
Optogenetics is a neuromodulation technique that combines techniques from optics and genetics to control and monitor the activities of individual neurons in living tissues. Axons corresponding to a particular modality or sub-modality are genetically modified to express light sensitive proteins for excitation or inhibition of the nerves when stimulated with light of a particular wavelength. See Lief Fenno et al. “The Development and Application of Optogenetics” Annua. Rev. Neurosci. 2011 34: 389-412. Unlike electrical stimulation, which will stimulate any and all nerves proximate to the electrode (hence the FINE and SC-FINE cuffs that flatten the nerve bundle), optogenetic stimulation can be targeted to a particular modality or sub-modality to provide the selectivity to interface with specific populations or subsets of axons within a nerve.
Chris Towne et. al. “Optogenetic Control of Targeted Peripheral Axons in Freely Moving Animals” PLOS ONE, August 2013 Volume 8, Issue 8 reports on methods to deliver opsins and light to targeted peripheral neurons for robust optogenetic modulation of motor neuron activity. As shown in FIG. 3, a biocompatible spiral cuff constructed from polydimethylsilloxane (PDMS) covalently bonded to a silicon-based optical fiber and terminated with a stainless steel ferrule were implanted into rats around the sciatic nerve. Light pulsed at 36 Hz with a pulse width of 5 ms and a power level of 20 mW was used to stimulate motor nerves in rats walking on a treadmill.